Separation of the constituents of gaseous mixtures



Nov. 23 1926.

c. c VAN NUYS- SEPARATION OF THE CONSTITUENTS 0F GASEOUS MIXTURES Filed oct. 22 4924 INVENTOR r M AATroRNEYS .Patented Noy. 23, 1926.

pairs!) STATES PATENT OFFICE.

- CLAUDE C. VAN NUYS, OE CRANFORD, NEW JERSEY, ASSIGNOR TO AIR REDUCTION" COMPANY, INCORPORATED, OF NEW YORK, N. 1., A CORPORATION OF NEW YORK.

SEPARATION OF THE CONSTITUENTS F GASEOUS MIXTU BES.

application filed October 22, 1924. Serial No."745.100

This invention relates to theseparation of ternary gaseous mixtures by liquefaction for the purpose of recovering the more imporr I tant constituents in a substantially pure conphysical characteristics similar to those of the ccnstituentsof air and that the invention is not limited, therefore, to the treatment of a specific gaseous mixture.

The invention isbased' upon the method and apparatus devised by Claude and constitutes an improvement thereon. In the Claude method air, for example, is first compressed and passed through a system of temperature exchangers whereby its temperature isreduced by heat interchange with cold gasous products of they separation. The en tering air is divided into two portions, the

larger of which passes to an expansion en-' gine wherein it is expanded with external work to accomplish a further reduction of temperature. The balance of the cold compressed air is delivered to a liquefier at its initial pressure a'ndis liquefied by heat exchange with cold gaseous products of the separation. The liquid and the cold expand ed air are delivered to'the column, beneath 'a tubular vaporizer wherein the unliquefied air is subjected tooheat exchange with accumulated bodies of liquid. Selective liquefaction. of-the air in the tubes as the result of this heat exchange produces a liquid en riched in oxygen which flows backwardly in the tubes and becomes more enriched by the 7 effect of backward return while the unliquefied residue passes upwa rdly from the" tubes. The liquid produced in the tubes of the vaporizer combines with the liquid from the liquefier and the combined liqpids are delivered to a rectifier in which t ey flow downwardly in direct contact with vapors arising from the body of liquid surrounding the vaporizer tubes. This causes a further b'fr enrichment of the liquid in oxygen by the separation therefrom of the more volatile constituent, nitrogen.

To ensure the morev complete separation of the constituents the unliquefied gaseous residue from the vaporizer tubes is liquefied by heat exchange with the liquids first accumulated in the bottomof the column and the liquid nitrogen thus produced is delivered to the top of the rectifier and flows downwardly. in contact with the rising vapors. More or less complete rectification is thus obtained, the descending liquid containing a large proportion of the oxygen originally present in the air while the gaseous effluent from the top of therectifier consists principally of nitrogen. The argon which is present in the air is divided and a portion remains with the liquid which accumulates around, the va orizer tubes while the balance escapes with t 1e nitrogen elllucnt.

The method as described can be employed with suitable regulation to produce suhstum tially pure oxygen or nitrogen in a similar condition. It is impracticable, however. to produce pure nitrogen 'andpnre oxygen in a single operation, partly by reason of the presence of approximately one per cent of argon in the entering air, but more particularly because the proportions in" which oxygen and nitrogen occur in air preclude the operation of the rectifier so that each is separated in a pure condition. -Thus, it pure oxygen is desired, the operation of the vaporizer is so regulated that a certain amount of oxygen will escape with the efliuent, ensuring that all of the nitrogen will leave the upper end of the rectifier and will not contaminate the oxygen liquid which accumulates around the vaporizer tubes. On the other hand, if pure nitrogen is desired it is found that the amount of nitrogen present in the air is not sufiicient to reflux all of the oxygen vapors. It is necessary there-- fore, to withdraw a portion of the accumulated liquid from the vaporizer at intervals. In the first case there is a loss of efiiciency due to the oxygen which escapes with the eflluent. In the second case there is a loss in efiiciency due not only to the removal ofthe liquid oxygen but also to the necessity of making up the refrigerative losses which accompany the withdrawal of the liquid. These refrigerative losses are met, in the Claude method, by increasing the pressure upon the entering air. 7

/ .tion of oxygen and nitrogenfrom air without o'sing any material portion of these constituents.

Further objects and advantages of the invention will be apparentas it is better understood by reference to the following specification and accompanying drawing in which gen or argon. 1s then recomprcssed with a shg it additional the preferred form of apparatus for carrying out the invention is illustrated diagrammatically. It is to be understood'that details of the apparatus which are well known to those skilled in the art are omitted for the purpose of clarity. The drawing is, therefore, indicative merely of the best arrangement of the essential parts of the apparatus.

In carrying out the invention the liquefaction and rectification are conducted in two successive stages, the primary operation being designed to separate a crude oxygen product containing the argon present in air and a small proportion of nitr ogenx The balance of 'the nitrogen in the air is separated in the primary operation and is recovered substantially uncontaminated witlfoxy- The crude oxy en product expenditure of power and'is subjected to a further liquefaction and rectification to separate the argon and nitrogen therefrom and i to produce a pure oxygen product including substantially all of the oxygen originally present in the air treated. It is possible thus to obtain pure oxygen and pure nitrogenfrom the air with an expenditure of power not substantially greater than that required to produce pure nitrogen alone in the operation of the Claude method.

The primary operation follows closely the procedure in separating nitrogen from the atmosphere according to the Claude method; that is, the air is compressed to a suitable pressure, e. g., 30 atmospheres, and cooled and a portion is expanded in an engine with external work while the balance is liquefied in the usual liquefier. The liquid is delivered to the column below the vaporizer tubes together with the cold expanded air and the latter is subjected in the tubes to backward return condensation to produce an enriched oxygen li uid which combines with that provided by t e liquefier. The combined li uids.

are delivered to themiddle portion 0 the rectifier and serve to liquefy the residual gas from the vaporizer tubes. The liquid nitrogen thus produced is delivered to the top-of the rectifier and acts as a reflux as it flowsdownwardly therethrough. The liquid which leaves the bottom of the rectifier and surrounds the vaporizer tubes is a crude oxygen product, the operation being so regulated that the argon and a small proportion of nitrogen remain in this liquid while a pure nitro en effluent escapes from the top ofthe recti er.

Crude oxygen vapor is withdrawn continuously from the space surrounding the vaporizer tubes, and after therefrigerative effect thereof has been utilized in suitable heat exchangers in the system this product is stored v in a suitable gas holder from which it is withdrawn and recompressed to a pressure of from three tofou'r atmospheres. This initiates the auxiliary operation in which the crude oxygen product is cooled to a suificiently low temperature preferably by heat exchange with cold products of the primary operation and is their delivered to the tubes of an auxiliary vaporizer to be there subjected again to backward return liquefaction wherein nitrogen and ar on are separated in the residual unlique ed gaseous mixture While the liquid produced becomes enriched in oxygen. This liquid is delivered to the middle portion of an auxiliary rectifier and serves first to liquefy by heat exchange the residual gaseous mixture from the vaporizer tubes. The liquid thus produced is utilized as a -reflux entering at the top of the rectifier and flowing down wardly therein to complete the separation of oxygen in liquid form from thevapors arising from the vaporizer. The result is an efiluent in which all ofthe argon and nitrogen in the crude oxygen product appear while the liquid which accumulates around the vaporizer tubes is substantially pure oxygen. The vap'or which is drawn from the space around the tubes is one of the products of the operation, the pure nitrogen havingbeen recovered as hereinbefore stated at the top of the primary rectifier.

Referring to the drawing, 5' indicates a coluinnwhich is divided by partitions 6 and 7 into compartments 8, 9 and 10. The air,

after it has been compressed and cooled, is

delivered through a pipe 11 to an expansion engine 12 where it is expanded with ex- Inn details of which will be described more fully hereinafter. The liquid produced passes through a pipe'16 controlled by a valve 17 to the compartment 8, being delivered preferably above a series of trays 18, such as are used commonly in rectification columns.

The expanded air enters beneath the trays and passes upwardly therethrough in contact with the liquid from the liquefier 15 and also with liquid produced in tubes 19 which extend through thrxcompartment'i).

Liquid is produced in these tubg by the selective liquefaction of the gaseous mixture rising from the trays 18, and joins the. liq-- uid flowing downwardly through these trays. The unliquefied-gas'eous residue from the tubes 19'cscapes to a head 2.0 and passes thence through a pipe 21 to a condenser 22 located in the compartment. 10. The gaseous residue liquefied in the condenser '22 by heat exchange with liquid Surrounding it is delivered through 'a pipe 23 controlled bya valve 24 to the upper end of the compartifient. 10. This compartment contains aplu- /rality of trays 25, such as are usually em-- ployed in'rectitiers, and the liquid reflux flows downwardly over the trays until it joins the liquid which is delivered from the compartment 8 through apipe'26 and valve 27 The combined liquids continue downward-1y over the trays while vapors rise therethrough from the compartment 9 where the liquid eventually accumulates on trays 25 surrounding the tubes 19.

By suitable regulation of the volume and pressure. of the entering gaseous mixture and of the flow of liquids through the apparatus, the desired separation -is accomplished in the rectifier and substantially pure nitrogen escapes as an efliuent from the top of the rectifier through a pipe 28. The liquid which accumulates'on the trays 25 and in the bottom of the compartment 9 is the crude'oxygen product. It is vaporized by heatexchange with the gaseous mixture in the tubes. .a portion of the vapor rising through the rectifier while another portion is withdrawn through a pipe 29.

The gaseous products of the separation are very cold and their refrigerative effect is utilized in the system'to cool the incoming' air and also to maintain the low temperature of the auxiliary cycle. The liquetier 15. com prising a shell enclosing a plurality of tubes 30 and 31, is thus utilized to liquefv a portion of the air. The crude oxygen'product escaping through the pipe 29 is delivered to a compartment 32 at one end of the liquefier and passes through the tubes 30 to a similar compartment 33 from which it passes through a pipe 34 to a compartment 35 at one end of an exchanger 36 comprising a shell enclosing a plurality of tubes 37 and 38. The crude o'xygen product passes from the compartment 35 through the tLlbes '37 to a corresponding compartment 39 at the o posite I end of the exchanger and is thence de ivered through a pipe 40 to a crude oxygen holder or gasometer 41. p The efliuentaescaping through the pipe 28 is, as wehave indicated, one of the substantially pure products of the operation. As it leaves therectifier it is at a relativel temperature and the refrigerative e ect is utilized to maintain the low temperature of the system. A' portion of this ,efiluent may be withdrawn through a pip'e42 which is conlow I eompartment44 at one end of the liquefier 15. It passes through the tubcs 31 to a corresponding compartmentAo at the opposite end of the liquefier and escapes thence through a pipe 46 to a compartment 47 at one end of the exchanger 36. It then passes through the tubes 38 in the exchanger to a compartment 48 at the opposite end thereof and is withdrawn through a pipe 49 and 'deliver-ed to a suitable storage receptacle (not shown). The balance of the efliuent passes through a pipe 50.to a compartment 51 at one end of an auxiliary liquefier 52, the function of which will be explained presently. This liquefier comprises a shell enclosing a plurality of tubes 53,- and after passing through the tubes the'efiluent is delivered by a pipe 54 to the pipe 42 and mixes with the portion which was withdrawn through the valve 43. All of the efiiuent passes thus through the liquefier l5 and exchanger .36 before it leaves the system and is brought thereby to substantially atmospheric temperature. Y 1

In passing through the exchanger 36 the products of the primary rectification cool the incoming gaseous mixture, for example, air, which enters the exchanger through a pipe 55 and circulates about'the baflles 56 in contact With the tubes 37 and 38. After being cooled the gaseous mixture is delivered by a pipe 57 to the pipes 11 and 14 leading to the ',the holder 41 through a pipe 58 and is compressed in a compressor 59 to a suitable pressure, e. g., three to four atmospheres. The compressor 1s provided with theusual water icooling devices (not shown). After compression and cooling the crude oxygen prod- .uct passes through a'pipe 60 to an-exchanger 61 comprising a shell and a plurality of tubes 62. The crude oxygen product travels about a plurality of baffles 63 in the exchanger and I escapes through a pipe 64 to the liquefier 52.

I t travels about the baffles 65 therein in conto the'cooling effect of the efliuent from the primary rectification. Owing vto the low fact with the tubes 53 and is thus subjected 1 crude oxygen product is partially liquefied and the liquid and vapor are delivered through a pipe 66 to acompartment 67 at the bottom of an auxiliary column 68. The latter column includes a vaporizing compartment 69 and a rectifier 70.

The vapor enteringthe compartment 67 passes upwardly through tubes 71 which are surrounded by liquid supported on trays 72" in the compartment 69. The liquid is evaporated and the resulting frigerative effect causes a selective liquefaction oghe vapor in the tubes 71. The liquid thus produced flows hackwardly through the tubes and -]O1I1S the fied gaseous resi ue continues to a head 72. The liquid in the compartment 67 1s delivered through the pipe 73 controlled by a valve M to an intermediate portion of the rectifier 70 and flows downwardly over trays 75 therein with resulting se' aration of nitrogenand argon, for examp e, and the 'pro-. duction of a liquid consisting substantially of pure oxygen. This oxygen passes through a pipe 76 to the compartment 69 and comprises the li uid' which is evaporated to maintain the re rigeration of the tubes 1. v j To ensure the maximum separation of nitrogen and argon the unliqnefied gaseous -residue frbm the head 7 2 is delivered through a pipe 77 o a condenser 78 within the rectifier 70. he gaseous residue is liquefied therein by\heat exchange withthe liquid in the rectifier and is delivered through a pipe 7 9 controlled by a valve 80 to-the upper end of the rectifier wherein it flows downwardly over the trays 75 therein. I

As the result of the rectificationhm efilucntconsistin argon is withdrawn through a pipe 81 and delivered to 'a compartment 82 at one-end of the exchanger 61. Passing thence through the tube 62' the eflluent isdelivered to a compartment 83. at the opposite end of the exchangerand to an outlet ipe 84.

' A portion of the vapors rom the bottom mtfthe vaporizer compartment 69.is withdrawn through a pipe 85 controlled by a valve 86 and delivered to a compartment 87 at one end of the exchangertl. These va pipe 89 which may be connected to a suitable storage receptacle (not shown). By the operation as described it is possi- Lhle to separate in a substantially continuous manner the two important constituents of a ternary gaseous mixture and tpreject an other constituent, the operationibeing conducted under conditions which permit a high efiiciency of separation. An important feature ofthe method is that one of the cold separa-ted products of the main cycle is conducted firstthi'oughthe auxiliary liquefier and has its temperature raised before it enters the primary liquefier. Consequently thequantity of primary cycle fluid condensed in the primary. .liquefier is reduced and'an increased amount thereof is available. for expansion in the engine and subsequent condensation in the tubes of the vaporizer. This permits the production of an increased amount of uncondensed residual nitrogen of the required purity which is available when liquefied in the condenser for subsequent use substantially of nitrogen and as-"a reflux liquid in the top of the primary rectifier. This increased uantity of reflux liquidin the com artment while the unlique makes it possible to vaporize'all of the liquid collecting in the lower level of the primary rectifier'and thus to increase the recovery of nitrogen. The cold which would be wasted otherwise in liquid rejected from the primary cycle thus serves to maintain the required refrigeration in the auxiliary cycle and consequently the power expenditiire'necessary to compress the gaseous mixture for the primary cycle is no greater when the auxiliary *cycle is emplo ed than when the Jrimar c 'cle is o ierate alone. In order to purify the crude ,oxygen product of the nitrogen cycle the only power expenditure necessary is that required to compress the crude oxygen product to 3 to 5 atmospheres. The quantity of crude oxygen prod-.

not to be purified is relativel small as com-- pared with-the quantity 0 the air from power necessary in the auxiliary cycle will e very small. 0

Various changes may be made in the details of operation and in the apparatus employed without departing from the invention or sacrificing any of the advantages thereof.

I claim 1. A method ofseparating the constituents of gaseous mixtures, which comprises producing a mixture in the gaseous phase impoverished in one of the constituents by a primary rectification, withdrawing the asewhich it is derived and it is evident that the ous mixture, re'compressing and lique ying the gaseous mixture, subjecting it to an auxliary rectification to separate. another constituent in substantial purity, and maintain in the low temperature of the auxiliary recti cation by the application of refrigera tion from the primary rectification;

2. A method of separating the constituents of gaseous mixtures,'which comprises producing a mixture in the gaseous phase impoverished in one of the constituents by a primary rectification, withdrawing and recompressingthe gaseous mixture, reliquefying the gaseous mixture-by heat exchange \Vlgl a product of the primary rectification,

an" subjecting the liquid to an auxiliary rectification to separate another constituent in substantiaPpurity. 4

3. A method of separating the constituents of gaseous mixtures, which comprises producing a mixture in. the gaseous phase impoverishedin one of the constituents by a primary rectification, withdrawing and recompressing the gaseous mixture, subjecting it to an ,auxiliary rectification to produce aliquid enriched in another; constituent and a gaseous efiluent, maintaining thelow temperature of the auxiliary rectification b application of refrigeration from the pr mary rectification, rejecting the efliuei'it and evaporating. the liquid by heat exchange with the recompressed gaseous mixture.

4. A method of separatin the constituents of gaseous mixtures, w ich comprises producing a mixture in the gaseous phase im verished in one of the constituents by a primary rectification, withdrawin the gaseous mixture, recompressing and iquefymg the gaseous mixture, subjecting it to an auxiliary rectification to separate another constituent in substantial purity, and utilizing excess'refrigeration from the priinary rectification to maintain the refrigeration in the auxiliary rectification. I .v v v 5. The method of separating the constituents of gaseous mixtures,,wh1eh comprises subjecting the compressed androoled' mixstituents, vaporizing the liquid, recompress-l ture to a primary liquefaction-and rectificas tion to separate a'gaseous' efil ent consisting of one of the constituents in'su stantial purity from a liquid containing all of the-coning thevapor, and subjecting the vapor to anauxilia liquefaction and rectification to separate a iquldconsisting of another'constituent in substantial purity from an efiluent mixture of the cqnstituents.

6. The method pf separatijngthe constituents of gaseous mixtures, which comprises subjecting the compressedand cooled mixture to a primary hquefaction and rectification to separate a gaseous eflluent consisting of one of the constituents in substantial purity from a liquid containing all ofthe constituents, vaporizing the liquid, recompressing the vapor, subjecting the va or to an auxiliary llquefaction and recti cation to separate a liquid consisting of another constituent in substantial purity from an efiluent mixture of the constituents and maintaining the refrigeration of the auxiliary liquefaction and rectification by heat transfer from the gaseousefiluent from the primary rectification.

ents of gaseous mixtures, which comprises subjecting the mixture to a primary liquefaction and rectification to separate a liquid impoverished in one of the constituents'and a gaseous efiiuent consisting substantially of that constituent, vaporizing the impoverished liquid to produce a gaseous mixture of similar composition, Sub ect'ing this gaseous mixture tg) recompression and an auxiliary liquefacti n and rectification, endincreasin the quantity of gaseous efiluent from t e first rectification by.'-v vithdrawin a portion of the refrigeration therefrom an 66' utilizing it to maintain the second rectifica ents of air, which comprises producing a "aseous mixture impoverished in nitrogen y a primary rectification, withdrawing the aseous mixture, recompressing and1l1quefying the gaseous mixture, and subjecting the liquid to an auxiliary rectification to separate a liquid consisting of substantially pure oxygen from an efliuent containing the remaining constituents present in the impoverished seous mixture".

9. A- met od of separating theconstitu ents of air, which com rises producing a gaseous mixture impoverished in nitrogen by a primary rectification, withdrawingthe gaseous mixture, recompressi'ng'and liqpefy mg the gaseous mixturasubjecting th 'quid to aniauxilia-ry rectification to separate a. liquid consisti "genjrom an efiient containing the remaining constituents present in the impoverished gaseous-mixture, and maintaining the auxiliary rectification by transfer of refrigeration from the primary rectification.

10. A method of separating the constituents of air, whichcomprises producing a aseous mixture impoverished in nitrogen y a primary rectification, withdrawing thegaseous mixture, recompre:s1ng and liquefying the gaseous mixture, subjecting the liquid to an auxiliary rectification to separate a li uid consisting of substantially pure oxygen rom an eliluent containing the remaining constituentspresent in the 1mpover-- iliary recti cation by the application of refrigeration from the primary rectification. -,12. In an apparatus for separating the constituents of gaseous mixtures, the combination of primary, and auxiliary rectification columns, means for supplying the gaseous mixture to the primary column, means for recompressing a gaseous product of the first rectification, means for delivering the recompressed gaseous product to the auxiliary rectification column and means for transferring refrigeration from another product of the first rectification to the auxil- 19.IP' rectification column.

11 testimony whereof I afiix my signature.

* CLAUDE C. VAN NUYS.

7 A method of separatin the constitumaintainin .the low temperature of the auxllll 

